The psoas (sō-ŏz) muscle is approximately 16 inches long. It begins at both sides of the 12th thoracic vertebrae of the back, and stretches all the way down to each of the legs, where it makes a final connection with the lesser trochanter. Also referred to as the "tenderloin," the psoas muscle is very thick and strong, and it is also the largest muscle found in the body.
This is a great picture I found that shows the structure and division of the spinal cord, along with all of its functions. Its very clear and simple - making it very easy to learn for nclex. And heres a tip for you - Ive seen many nclex practice questions that focus on Spinal Cord Injury affecting C1-4, which affect breathing.